The present invention relates to copending, commonly assigned U.S. patent application Ser. No. 07/854,146, filed Mar. 20, 1992, now U.S. Pat. No. 5,438,709 entitled "Lubricous Gloves and Method of Making Lubricous Gloves".
Plaster of Paris casts have been used to immobilize body members for some time. These bandages are made by depositing plaster of Paris on a reinforcing scrim material such as gauze. When the plaster of Paris is dipped in water, reactions take place which result in the hardening of the cast material. Plaster of Paris casts, however, suffer from a number of disadvantages. X-ray transmission through the cast to determine whether a fracture has properly set is extremely difficult. In addition, the cast is quite heavy and restricts the mobility of patients wearing the cast.
In order to overcome the disadvantages of plaster of Paris casts, numerous attempts have been made to develop plastic or plastic-reinforced material as replacements for plaster of Paris. U.S. Pat. Nos. 3,241,501 and 3,881,473 disclose casts which are made with a flexible fabric impregnated with a polymer which is capable of being cured by ultraviolet light.
Other attempts to replace plaster of Paris casts are disclosed in German Offenlegenscrift Nos. 2353212 and 2357931, U.K. Patent No. 1,578,895 and PCT Application No. WO81/00671. These casting tapes are open-weave fabrics coated with polyurethane prepolymers, that is, reaction products of isocyanates and polyols. The tapes are dipped into water in the same manner as the plaster of Paris and then applied to the limb of the patient. The water causes the prepolymer to polymerize and form a rigid polymer structure.
More recently, it has been found that in working with such materials having prepolymer resin coating that the tackiness of the resin of the tapes can make working with the tapes difficult and cumbersome for the doctor. In an attempt to address this issue, a glove lubricant comprised of water, sorbitol, mineral oil and silicone fluid has been sold by 3-M Company, St. Paul, Minn., under the tradename Cast Cream.TM. with instructions to apply the lubricant to the gloves of one applying an isocyanate-functional prepolymer coated cast after wrapping of the cast but before molding of the cast to avoid having the exposed casting material adhere to the gloves of the one applying the cast. This is disclosed in the background of U.S. Patent Nos. 4,667,661 and 4,774,937.
The '661 and '937 patents are directed to addressing the adherence issue by providing the resin itself with a lubricant. The curable resin-coated sheet is prelubricated with a lubricant which is either a) bonded to the resin; b) added to resin or applied to the surface of the coated sheet; or c) provided in a combination of the bonding and surface application described. In many instances, however, the tacky feature of the orthopaedic casting tape is desirable. As by way of example, when the applier is attempting to get the end of the tape or bandage to stick to the surface of the casting tape wrap in order to terminate the application of the tape. The addition of lubricant in the resin permits relative slipping of the resin-coated sheet but requires molding the cast in position and holding it in position to prevent slippage.
Coatings for substrates having a lower coefficient of friction have been shown in U.S. Pat. No. 4,100,309 entitled, "Coated Substrate Having a Low Coefficient of Friction Hydrophilic Coating and a Method of Making the Same". That reference describes a substrate which is coated with a polyvinylpyrrolidone-polyurethane interpolymer. Copending commonly assigned U.S. patent application Ser. No. 726,449, now U.S. Pat. No. 5,439,439 filed Jul. 8, 1991, entitled, "Method of Applying an Orthopaedic Bandage" discloses the use of a polyvinylpyrrolidone coated glove in the application of resinous substrate casting materials. Although the invention described in that application represents a significant advance in the science of orthopaedic casting tapes, there have been certain shortcomings discovered regarding those gloves. That is, the slipperiness of the gloves is present to such a great extent that ancillary manipulation is restricted. The ability of the applier of the casting material to handle pens and other utensils or to tear open foil packages to access the casting material is greatly restricted by the extreme slipperiness of the gloves. Certain other lubricous gloves, for example, polyvinylpyrrolidone-polyurethane coated gloves may have such a slippery surface that handling of the tape roll itself was clumsy. Furthermore, the durability of the gloves is at a point that is less than optimum.
For example, gloves may lose the slippery characteristics completely after applying a few rolls of fiberglass casting tape. Often on large casts multiple tapes must be applied to create a finished cast structure. Thus, the practitioner would have to change gloves in the middle of wrapping a cast which is inconvenient. This loss of functionality is partly due to poor adhesion of the top coat to the base elastic glove, such as natural rubber glove. Also, the elastic modulus of the top coat and the substrate may be widely different. In particular, during the glove making process, stripping of the coated natural rubber glove requires the glove to be stretched greatly. In this case, delamination of the top coat may occur at places where the stretch was the greatest. The same kind of delamination may take place while donning the glove. The delaminated spots are often the areas that show the loss of slip and result in portions of the glove sticking to the casting material during the wrapping process. The delamination is more frequent with a stiffer top coat than with a more flexible top coat. In many cases, portions of the delaminated area are separated entirely from the glove surface exposing an unlubricated glove surface to the casting material.
Poly(vinyl alcohol) (PVA) coated gloves have been found to have outstanding durability and slip characteristics. However, the preferred, or most effectual thermally reversible gelling agent used in existing poly(vinyl alcohol) glove manufacture is toxic and not applicable to medical gloves.
Commonly assigned U.S. patent applications Ser. No. 07/854,146, mentioned above describes a poly(vinyl alcohol) coated glove used for applying casting material which has a thickener added to the coating in order to improve the processability and use of the coating.
It is known that a number of hydrophilic polymers exist which have been used to provide a lubricated surface for applications such as catheters and guidewires used in medical applications. These applications traditionally use polymers such as PVP and PEO which are known to provide a lubricous surface when in an aqueous environment. A problem typically encountered with these polymers is the loss of slippery properties due to a combination of the solubility of these polymers in water at ambient temperatures and the wear which they experience in use. In order to improve the performance or longevity of these coatings, crosslinking has been used to provide a chemical bond which would lead to a coating with reduced water solubility. This has been accomplished using polyisocyanate reagents (U.S. Pat. Nos. 4,100,309; 4,119,094 and 4,550,126), high energy radiation [A. Henglein, Journal of Physical Chemistry, 63, 1052 (1959)]as well as a free radical initiators [British Patent No. 1,022,945, and C. C. Anderson et al., Journal of Applied Polymer Science 23, 2453-2462 (1979)].
Hydrophilic coatings which do not require chemical modification have been disclosed (U.S. Pat. No. 4,977,901). These are based on the ability of the polymer to crystallize on heat treatment such that the crystallites serve as physical crosslinks and prohibit the dissolution of the coating when in contact with water at ambient temperatures, even when the coating is subjected to frictional forces. The crystallization of polymer coatings results from the inherent chemical structure of the polymers and thus is limited to a small group of polymers. A common semi-crystalline polymer which also exhibits slippery properties when in an aqueous environment is PVA. PVA possesses uncommon solubility properties in that it only dissolves in water at elevated temperatures due to the strong hydrogen bonding between polymer chains in the dried state.
Although PVA can be used to provide a lubricous surface and serve effectively in applications such as casting gloves and other articles requiring a hydrophilic surface, the semi-crystalline nature of this polymer as well as its hydrogen bonding capability result in physical properties characterized as stiff, brittle, and inflexible. As a result, coating flexible articles with PVA results in a stiffening of the flexible substrate and may lead to an alteration of the performance of such article. In the case of a latex casting glove, the stretchability of the glove is severely reduced resulting in the alteration of the intended size of the glove as determined on the form from which it is made. For example, a large sized latex glove is reduced in size to that of a medium when coated with a PVA coating. Additionally, the processing of the gloves coated with PVA is complicated due to PVA's stiffness which can lead to abnormally slow production rates and a high defect rate when the gloves are manually removed from the glove forms. Furthermore, the stiff coating prohibits the use of automated glove processing technologies which remove the glove from the hand form by air jets which partially inflate the gloves.
PVA may be made flexible by using a number of chemical plasticizers, such as water, glycerin, ethylene glycol, Urea, ethanolamines, and other glycols and diols. In addition, humectants have also been used to flexibilize PVA by virtue of their water absorbing properties and the fact that water is the most effective plasticizer for PVA. Glycerin has been widely used as a plasticizer for PVA due to its low toxicity and its low vapor pressure compared to water, ethylene glycol, or others. The addition of glycerin leads to a softening and thus enhances the flexibility of PVA, especially in the case of PVA films. It has been found, however, that some glycerin can evaporate during a high temperature processing. Even in the presence of glycerin, it has been observed that low humidity conditions lead to a glove coating with poor flexibility and undesirable physical properties. In addition, it has been determined that although high levels of glycerin lead to more flexible PVA films, it also leads to a softening of these films, and to an enhancement of their solubility in water at ambient temperatures. This is especially true where the films are exposed to frictional forces where abrasion can quickly destroy the film. U.S. Pat. No. 4,608,187 describes the rubber toughening of PVA film compositions through the blending of rubbery materials with a glass transition less than 9.degree. to -18.degree. C. to form flexible PVA pouches or envelopes used to deliver detergents in laundering applications. This disclosure describes that the PVA rubber blends result in the formation of discrete, rubbery microdomains which provide the PVA with a significant increase in flexibility. It is further disclosed that the mechanism of rubber toughening is believed to be related to the partial incompatibility of the PVA and rubber resulting in microscopic crazing of the PVA/rubber blend matrix leading to improved low temperature flexibility.